The present invention relates to a process and an apparatus for joining polymer materials at a high welding speed.
It is known to join polymer materials by means of laser beams in that the upper material, facing the laser beam, is shone through by the latter and, at the contact surface between the upper material, which is transparent to the laser beam, and the lower material, which is opaque to the laser beam, the two materials are heated and joined to each other under pressure. The material that is transparent to the laser beam may be optically black in the visible wavelength range. In addition, for this purpose it is known to produce a linear laser beam, a relative movement between the materials and the laser beam taking place during the welding operation in order to produce the desired welding contour.
A precondition for the welding process according to this transillumination technique is the thermal response of the polymer under IR irradiation. The polymer, pigmented with IR-absorbing substances, absorbs the thermal energy from the IR source (laser source) under irradiation and is heated. The accumulation of the thermal energy and the temperature therefore reached in the polymer depend on the manner in which the energy is metered, such as energy density and irradiation time, for example. In addition, the material characteristics, such as the thermal conductivity, for example, are of significance. The critical step for the welding process is the phase transition between the solid body state into the liquefaction state, which is also referred to in the following text as the melting temperature. In order to reach this melting temperature, a certain heating time is needed, because of the low thermal conductivity of the polymer. In principle, it is possible to implement a shortening in the irradiation time with a correspondingly high energy rate. However, this measure reduces the size of the process window in which individual adaptation of the process parameters is possible and, as a result, has a considerably adverse affect on the welding quality.
Endless film material can be used, for example, as part of a micromechanical component, sensors, actuators etc., the film material also being the transport means for the component at the same time. In addition, endless film material can be used for packaging such components transported on a film or other objects to be packaged. In order to produce welded endless films of this type, it is important to implement a welding operation that is as accurate as possible but also fast.